An actuator unit for an injection valve of an internal combustion engine of a vehicle typically comprises a component in the form of a stack that comprises a plurality of electrode layers as well as a plurality of layers of material that react to the application of an electric field, wherein each layer of material is disposed between two of the electrode layers. Such a component of layers stacked one above the other and comprising alternating layers of material and electrode layers is generally referred to as a stack. The currently best known electronic component of this type is generally a stack referred to as a piezoelectric actuator, which is used as an actuating element in injection valves of diverse engine types for motor vehicles. The layers of material are ceramic layers in said piezoelectric actuator.
Such a stack usually comprises a rectangular or square cross-section when observed in plan view. The stack is typically electrically contacted on two mutually opposing peripheral sides. In order to be able to perform this carefully in a technological sense, the electrode layers are configured geometrically for example such that only every second electrode layer extends laterally to one of the two peripheral sides, whereas the respective other electrode layers do not extend to said peripheral side. The same applies to the other peripheral side of the stack.
The electrical contacting of the electrode layers is performed by means of two outer electrodes, which are generally electrically connected to respective electrode layers on at least one peripheral side of the component and typically on two mutually opposing peripheral sides.
The finished component is enclosed by a tubular spring, which typically consists of a metal. The tubular spring is used to pretension the component stack during operation of the actuator unit and thereby to prevent damage to the ceramic. The tubular spring is also used to provide a restoring force for the deflected component stack. A layer, for example of silicon, which covers at least the outer electrodes, is provided on the component stack on the outer peripheral side as insulation material between the tubular spring and the outer electrodes of the component stack.
With increasing requirements on emissions and consumption, the requirements on the injection of the fuel into the combustion chamber are increasing. Higher pressures, temperatures as well as multiple injections consequently require higher accuracy in the metering of the injected fuel. In order to achieve the required accuracies, it is therefore not sufficient to operate the actuator in an actuating mode. Rather, regulation is required. For regulation, defined measurement variables are required, which are determined on or in the actuator unit, in order to calculate therefrom the corresponding regulation variables.
For example, sensors can be used for this that directly detect the opening and closing time point of a needle of the injection valve actuated by the actuator. Such a sensor can for example be a piezoelectric force sensor that is coupled to the piezoelectric actuator in a force-fit manner. The measurement accuracy that can be achieved here is, however, not high enough for precise regulation.